Radiant energy controlled oscillator



Dec. 5, 1967 J. FORMA-N RADIANT ENERGY CONTROLLED OSCILLATOR Filed Nov. 1964 2 Sheets-Sheet l INVENTOR.

2 Sheets-Sheet WIFA/f/T/ Dec. 5, 1967 Filed Nov. 1964 momg INVENTOR. JX/t/ FflF/WAA/ United States Patent 3,356,964 RADIANT ENERGY CONTROLLED OSCILLATOR Jan Forrnan, 10548 Eastborne Ave., Los Angeles, Calif. 90024 Filed Nov. 2, 1964, Ser. No. 408,053 13 Claims. (Cl. 331-66) ABSTRACT OF THE DISCLOSURE There is described a photo-tube device which generates low frequency coherent oscillations due to an electron bunching effect caused by a periodic or discontinuous pattern of light falling on the cathode. There is a magnetic field applied to the photo-tube having a component of flux extending across the region between the anode and cathode. No electrical energy source is required in the circuit. The frequency of oscillation is proportional to changes in the intensity of the light falling on the phototube.

This invention relates to a unique oscillator circuit and, more particularly, is concerned with an oscillator circuit which is set in oscillation by incident radiant energy and which oscillates at a frequency which is dependent on the intensity of the incident radiant energy.

I have found that a vacuum photo-tube having a photoemissive cathode can be used as an oscillator when suitably excited by a source of radiant energy, such as visible light and when the photo-tube is subjected to a suitably oriented magnetic field. While the nature of the phenomenon is not fully understood, it is believed to involve a rotating electron plasma within the region between the anode and the cathode electron emissive surfaces with which the electrodes are capacitively coupled. The rotation of the plasma is produced by the combined effect of the magnetic field and the effect on the emission of the cathode by the pattern of the incident light.

In brief, it has been found that an ordinary vacuum phototub having a semi-cylindrical cathode or emitter and a rod-shaped anode or collector can operate as an oscillator for generating an alternating signal of at least 300 millivolts in amplitude across a load resistor connected between the cathode and anode. No applied potential between the cathode and anode is necessary, although a potential of a few volts improves the stability and dynamic range of the oscillator. A magnetic field is required having a component of flux extending across the region between the anode and cathode which is generally parallel to the plane defined by the two parallel linear edges of the semi-cylindrical emitter of the photo-tube. When the cathode is partially illuminated by a strip, a pattern of strips, or spot of light or when a strong shadow is cast on the cathode which divides the cathode into at least two illuminated portions, strong oscillations are generated. It is believed that the separation of the cathode into separate emitting regions permits bunching of electrons in the magnetic field analogous to the bunching of electrons in the gaps of a magnetron anode.

There are, in fact, several possible modes of oscillation that have been observed. In the principal mode of operation, the outputv signal is sinusoidal and varies linearly in frequency with changes in light intensity. This mode is induced by a sharply defined beam of light striking a portion of the cathode. In another mode of oscillation, low frequency oscillations are produced which are non-sinusoidal in form and in which the frequency of oscillation is much more sensitive to the strength of the magnetic field. This mode is induced by a shadow having more diffuse boundaries which divide the cathode into at least two larger illuminated areas. A very high frequency mode of oscillation has also been observed by using a choke across the output to effectively short out the low frequency oscillations.

For a more complete understanding of the invention, reference should be made to the accompanying drawings wherein:

FIGURE 1 is one embodiment of the present invention;

FIGURE 2 is another embodiment of the present invention;

FIGURE 3 is yet another embodiment of the present invention;

FIGURE 4 is a modified embodiment of the arrangement of FIGURE 3;

FIGURE 4a is an alternative arrangement to that of FIGURE 4.

FIGURE 5 is a graph illustrating the operating characteristics of the oscillator of the present invention;

FIGURE 6 is a schematic showing of a further modification of the present invention; and

FIGURE 7 is a graph illustrating another operating characteristic of the oscillator of the present invention.

Referring now to FIGURE 1, there is shown in outline an evacuated envelope 1 of a tube having a photo-emissive planar cathode or emitter 2 and a frame-like anode or collector 3, this collector lying generally in a plane parallel to the emitter 2. A magnetic field generally parallel to the plane of emitter 2 is established by means of a permanent magnet having poles 4 and 5 symmetrically placed on opposite sides of the tube. The emitter is illuminated by a narrow band of light 6 by any suitable means such as the combination of the light source LS. and the slit in a stop 7. The shape and size of the collector 3 is preferably such that it casts no shadow on the emitter.

The emitter 6 may have any surface material which ejects electrons when subjected to radiation or atomic particles, and the light source LS. may be any source of radiation or radio-active particles to which the emitter material is sensitive. For example, with a tube having a cesium coated emitter mentioned above and illuminated by white light from a low power incandescent lamp, it has been found that with a field of approximately 200 gauss, a pure sinewave output of up to 4 millivolts peak to peak is obtained.

There is a direct linear dependence of frequency upon the intensity of illumination on the emitter, as shown by FIGURE 5. With a given magnetic field, the amplitude of the signal remains the same for different values of light intensity within broad limits as long as the impedance of the load is matched with the impedance of the tube. The frequencies available from the device shown in FIGURE 1 range from about 10 c.p.s. to at least kc./sec. depending only on change in light intensity. This makes the device useful for measurement of illuminance in terms of frequency As shown in FIGURE 7, the frequency is inversely proportional to the strength of the magnetic field. Thus for strong magnetic fields, the frequency is not sensitive to small variations in magnetic field.

FIGURES 2 and 3 show variations of the light pattern and the electrode structure shown in FIGURE 1.

The device shown in FIGURE 2 differs from that shown in FIGURE 1 in that the stop 7 bears a plurality of slits rather than only one. FIGURES 1 and 2 illustrate that the circuit oscillates in the same fashion with striated light, a single strip, or even a spot of light. The circuit does not oscillate with uniform illumination of the cathode.

FIGURE 3 shows an arrangement in which the electrodes take the usual form of a photo-tube, the emitter 12 being a portion of a cylinder. The magnetic field set up by magnetic poles 14 and 15 is generally transverse to the rod anode 13 and is parallel to the plane defined by the two linear edges of the semi-cylindrical cathode. A strip 16 has a different illuminance than the, rest of the emitter. The strip consists of the shadow of the collector 13. This figure illustrates the fact that a difference between. the illuminance of the strip 16 and the rest of the emitter is sufiicient to effect oscillation. It has been observed that witha distant light forming a somewhatdiffuse shadow, a different mode of oscillation exists which is lower in frequency and in which the wave form is typically non-sinusoidal. However, in this mode the frequency is less stablewith changes in field intensity.

A resistive load has been shown in all the figures with the emitter being grounded to reduce stray field pickup. It has also been found that if the output is taken across a choke coil whichfilters out the lower frequencies, oscillations in excess of 2.5 megacycles can beobserved which alsochangein frequency with-light intensity. It is significant that the load does not affect the frequencyof oscillation and therefore a tuned circuit could be used in place of the resistive load if desired.

As previously mentioned, the device has a constant amplitude output when the load matches the impedance of the device over the rangeof operation. Since the deviceis believed to rely for its operation on an interelectrode rotatingIelectrOn. plasma with whichthe electrodes are. capacitively coupled, the effective impedance ofv the device changes with the magnetic field strength.

The effective impedance isalsoinversely proportional to the illuminance. Bearing this in mind, it will be apparent that a photo resistor, such as a cadmium sulfide ele ment, or a pair of photo. tubes oppositelyconnected inparallel, would provide the required impedance matching if their illumination varied in the same manner as. the illumination :of .the present. device. An arrangement. working on this principle is shownin-FIGURES-4and 4A. The device is identicalto that shownin FIGURE 3 and its load consists of two photo tubes 19 and20 oppositely connected in .parallel, the output 18-being takenqacross.

these photo tubes. The photo tubesare illuminated by thelight source L .S.-whichilluminates the device. Al,

though shown on the opposite sideof light source L.'S.,

the photo tubes liland 20 could, of course, be.positioned on the sameside. of the light source. By using a photo.

resistor which hasthe. same conductivity in either direction, v the arrangement .of FIGURE 4A.. is provided in which a single photo resistor 19A replaces the two phototubes required inthe circuitofFIGURE'4. The circuit is otherwiseidentical to the oscillator circuit of FIGURE 4.,

FIGURE 6-illustrates .another important aspect of the present invention. If the light source L.S.. passed through aslit in the plate 17 and focused on one edge of the cathode 12 of a photo-tube,oscillations are produced at the output. 18 across the load resistor R. If, in addition, there is ageneral, illuminationof the cathode '12 by background; illumination, such as a bulb 22 and a diffusing screen23, the frequency ofthe-output canbecontrolled by. the llevelofillumination of the diffuse source as well as .the intensity ofthestrip source..Thus-a mixer is provided which canbe used ,as amodulator ora demodu-v lator. For example, a circuit, suchas an amplifieror the like, can be used to vary the intensity of the bulb 22 withvariations in amplitudeof an inputsignal.

While the oscillator is. generally described as preferably operating with zero anode potential, the amplitude of the output may be increased to a maximum of several hundred millivolts with two or three volts positive potential on the anode. A small positive potential of several volts, as indicated in FIGURES 2 and 3, increases the dynamic range of the oscillator, enhances the stability and increases the output amplitude. Variations in the anode potential over a range of 1 to 5 volts produces very little change in output frequency. Other factors such as the frequency (color) of the light source, the character of the light pattern and the sharpness or diffusion of the light image, all affect the. characteristics of the oscillator. Also the invention is applicable to use with other-types of radiant energy, such :as infrared, ultra-violet or X-ray radiation, as well as alphaandbetaparticle radiation, depending on the spectral sensitivity of-the emitter.

What is claimed is:

1. An oscillator for generatingan alternating output signal comprising a cathode having an electron emissive surface sensitive to incident radiant energy, an anode positioned infront of the cathode electron. emissive surface,

means for enclosing the anode and cathode in a vacuum pedance connected between the anode and the cathode across which the oscillating output signal is generated,

2. Apparatus as defined in claim-1 wherein said means connected between the anode and cathode includes-conductors for directly connecting the output load impedance to the anode and cathode.

3. Apparatus as defined in claim 1 wherein said means connected between the anodeand the .cathodeincludes a potential source of not more than a few volts connected in series with theload impedance between the anode and cathode to provide a small DC voltage between theanode and cathode.

4. An oscillator circuit comprising a vacuum photo-tube having a light sensitiveemitter and collector Within an enclosure, means for illuminatinga portionof the emitter surface with an elongated area with a different level of illumination than the adjacent portion of the emitter, meansproducing a magnetic field extending transverse to the elongated area in the region between the emitter and collector, and a load impedance connected between the emitter and collector, the oscillator output signal being derived across the impedance.

5. Apparatus as defined in claim 4 wherein said means. illuminatinga portion of, the emitter includes means for forming an elongated strip of light focused on the emitter.

6. Apparatus as defined in claim 4 wherein said meansilluminating a portion of the emitter is positioned to cast a shadowcf the collector on the surface of the. emitter.

7. Apparatus as defined in claim .4awherein said inpedance is a resistor.

8. Apparatus as defined inclaim 4 wherein said impedance is. a light. sensitive element having an effective resistance that changes with light intensity.

9. An oscillator comprising a vacuum photo-tube having a semi-cylindrical cathode. and a rod-shaped anode within anenclosure, means for directing a beam of light at the cathode, said beam of light being formed to il- Iurninate only a portion of the cathode surface, means for producing a constant magnetic field in a direction parallel to the plane defined by theparallel straight edges of the semi-cylindrical cathode and perpendicular to the rod shaped anode, and a load impedance connected to the anode and the cathode.

10. Apparatus. as defined inclaim 9 further includingv means for applying a small DC potential between the cathode and the anode.

11. Apparatus as defined in claim 9 wherein the. load impedance is a resistor substantially matching the anodet-o-cathode impedance of the. photo-tube.

5 12. Apparatus as defined in claim 9 further including means simultaneously providing illumination of the cathode with incident energy at a different energy level than the beam of light.

13. Apparatus as defined in claim 12 further including means for varying the intensity of illumination of said illumination providing means.

References Cited UNITED STATES PATENTS 2,244,318 6/1941 Skellett 33166 X 6 2,424,933 7/1947 Kalmus 332-3 X 2,777,954 1/1957 White 331-66 3,258,597 6/1966 Forrester 250-199 NATHAN KAUFMAN, Acting Primary Examiner.

ROY LAKE, Examiner.

10 J. MULLINS, Assistant Examiner. 

1. AN OSCILLATOR FOR GENERATING AN ALTERNATING OUTPUT SIGNAL COMPRISING A CATHODE HAVING AN ELECTRON EMISSIVE SURFACE SENSITIVE TO INCIDENT RADIANT ENERGY, AN ANODE POSITIONED IN FRONT OF THE CATHODE ELECTRON EMISSIVE SURFACE, MEANS FOR ENCLOSING THE ANODE AND CATHODE IN A VACUUM REGION, MEANS FOR DIRECTING RADIANT ENERGY IN AN ELONGATED PATTERN ON THE ELECTRON EMISSIVE SURFACE OF THE CATHODE TO PROVIDE AN ENERGY DISCONTINUITY ON THE CATHODE SURFACE, MEANS FOR PRODUCING A MAGNETIC FIELD EXTENDING IN A DIRECTION TRANSVERSE TO THE ELONGATED DIRECTION OF THE ENERGY DISCONTINUITY, AND MEANS INCLUDING AN OUTPUT LOAD IMPEDANCE CONNECTED BETWEEN THE ANODE AND THE CATHODE ACROSS WHICH THE OSCILLATING OUTPUT SIGNAL IS GENERATED. 